fix(deps): update dependency socket.io to v2.2.0

Author: renovate[bot]

appengine/websockets/package.json

@@ -19,7 +19,7 @@
   "dependencies": {
     "express": "4.15.4",
     "pug": "2.0.3",
-    "socket.io": "2.0.3"
+    "socket.io": "2.2.0"
   },
   "devDependencies": {
     "@google-cloud/nodejs-repo-tools": "1.4.17",